1. Field of the Invention
This invention relates to optical digital matrix multiplication apparatus and, in particular, to apparatus for performing digital matrix multiplication using cavityless optical bistability. Accordingly, it is a general object of this invention to provide new and improved apparatus of such character.
2. General Background
Traditionally, optical techniques have been based on analog operations such as Fourier transforms performed by lenses and acousto-optic devices. More recently, however (see H. J. Caulfield, J. A. Neff and W. T. Rhodes, "Laser Focus/Electro-optics", Nov. 1983, p. 100), attention has been turned toward the application of optics to mathematical operations. There, operations are numerical, sometimes discrete, and often algebraic in character. The high degree of parallelism available in optics has led to the recent development of non-programmable array processors in which a 100 component vector can be multiplied by a 100.times.100 matrix in about 20 nanoseconds. Components of an input vector x can be inputted via a linear array of LEDs or laser diodes. The light from each source can be spread out horizontally by cylindrical lenses, optical fibers, or planar lightguides to illuminate a two-dimensional mask that represents the matrix A. Light from the mask, which has been reduced in intensity by local variations in the mask (transmittance function), is collected column by column and directed to discrete horizontally arrayed detectors. The outputs from such detectors represent the components of an output vector y, when y is given by the matrix-vector product y=Ax. Such a device, however, suffers from several potentially serious limitations, including limited accuracy with which the source intensities can be controlled and the output intensities read; the matrix A cannot be updated rapidly.
Thus, it is well known to utilize a plurality of input sources such as light emitting diodes having intensities that apply light through cylindrical lenses onto a photographic matrix such as a mask or film. For example, let us consider a 2.times.2 pixel mask. The point sources of light from the light emitting diodes are displayed as lines on the mask, vertical lines for example. Then light from the top half of the photographic plate is displayed onto a plurality, such as a pair, of vertically disposed detectors by way of a horizontal cylindrical lens so as to converge the upper half of the light from the photographic plate to a point source, or pixel, at the detector Y.sub.1.
Similarly, for X.sub.2 intensity, from a second LED, light would be displayed at the right half portion of the photographic mask, via a vertically disposed cylindrical lens. And light from the bottom half of the mask can be supplied therefrom through a horizontally oriented cylindrical lens to the bottom half of the detector. All of the foregoing is well known in the prior art.